What is SMA?

    SMA stands for Shape Memory Alloy made of high strength nickel and titanium. Shape Memory Alloys have a unique property compared to most other metals in that they can be “trained” to remember a certain shape. This shape can be recalled through heat activation. When heat is applied to the metal, the crystalline structure of the metal changes from martensite to austenite creating a physical structural shift. Since SMA has an ability to “remember” a shape, we also refer to it as “Smart Metal”. The following video demonstrates the amazing properties of SMA wire.

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    To apply SMA into an optical image stabilization device, HTI has partnered with Cambridge Mechatronics (CML). CML is a design and engineering company based in Cambridge, England. CML designed and patented their SMA OIS actuator solution and sought HTI out as a world-class development and manufacturing partner to complete development and scale OIS into mass production. HTI and CML entered into a collaboration agreement in 2013 and since have been jointly developing SMA OIS actuators that HTI now mass produces.

SMA OIS Camera Design

    The SMA OIS actuator is placed between the traditional Auto Focus (AF) actuator and the image sensor. SMA OIS actuators can be customized to match almost any existing AF design and technology providing smartphone and camera module makers with a variety of AF & supplier choices.

Gemini SMA OIS Design:

In the race for better camera performance and thinner smartphones, having the thinnest camera is essential to industry leading smartphone designs. Gemini, our latest “Smart Metal” optical image stabilization (OIS) actuator, reduces OIS actuator thickness by 70% over previous SMA products to enable the world’s slimmest OIS smartphone camera designs. The unique properties of Shape Memory Alloy (SMA), or “Smart Metal”, enable a high performance, rugged, small, yet simple actuator design. The elegant design cuts the component count in half from the previous SMA products and is designed to leverage our existing TSA+ flexure process capability and assembly capacity to reduce investment and enable fast customer ramps. The Gemini design, in combination with our automated processes, quality control systems, and high-volume precision manufacturing capabilities position us well to support large smartphone programs.

How Does a SMA Actuator Work?

    The SMA OIS structure is quite simple. It primarily consists of a fixed plate and a moving plate separated by planer bearings. The autofocus lens is attached to the moving plate and the fixed plate is attached to a baseplate which is fixed to the image sensor bracket. SMA wires are connected between the fixed and moving plate on each of the 4 sides. The tiny (25 micrometer) SMA wire (about 1/3 of the thickness of a human hair) is used as the “motor” to move the top plate and attached autofocus lens mechanism to compensate for hand shake. The SMA wire has been preconditioned to be at a shorter condition when heat is applied. When a small amount of current is applied to a wire by the controller chip, the wire heats up and shortens to pull the actuator to one side. When the wire cools, the wire stretches back out. Since we use such small diameter wire this transition happens very quickly enabling a responsive system with plenty of bandwidth to suppress human hand shake. Each wire is individually addressable by the controller chip. By sending different current to each wire, the actuator can be moved in any direction and rotation can be controlled. As each wire shortens it also increases in diameter and therefore reduces the resistance in the wire. The controller chip continuously measures the resistance in each wire and uses that information to control position of the actuator with submicron resolution without the use of extra position sensors.